Blog Archives

What percentage of electronic failures are latent defects? What’s the cost to industry? According to the ESD Association “It is relatively easy with the proper equipment to confirm that a device has experienced catastrophic failure. Basic performance tests will substantiate device damage. However, latent defects are extremely difficult to prove or detect using current technology, especially after the device is assembled into a finished product.” So there is the view that, by definition, it is impossible to quantify the amount of latent damage. However, for most companies, the cost of customer returns and field service warranty expense greatly exceeds in-house scrap & re-work expense.

Per the ESD Association: “The age of electronics brought with it new problems associated with static electricity and electrostatic discharge. And, as electronic devices became faster and smaller, their sensitivity to ESD increased. Today, ESD impacts productivity and product reliability in virtually every aspect of today’s electronics environment. Industry experts have estimated average product losses due to static to range [up to] 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually.”

Some major companies report that 25% of all identified electronic part failure is due to ESD. As an ESD Control Program improves, a resulting decrease in unidentified field failures and ”no problem found” returns should occur. Reducing latent defect field failures is what allows companies to report return on investments of 10:1 from their ESD Control Programs.

It may seem to some that CDM has newly arrived as a problem for ESD control programs. However, the ESD Association first published ANSI/ESD STM5.3.1 in 1999 – ESD Association Standard for Electrostatic Discharge Sensitivity Testing – Charged Device Model (CDM) – Component Level. Basically, CDM testing has to do with “testing, evaluating and classifying the electrostatic discharge (ESD) sensitivity of components to the defined charged device model (CDM)” … “to allow for accurate comparisons of component CDM ESD sensitivity levels.”

The importance of CDM came about primarily because of the increased use of automated component handling systems. The Foreword of ANSI/ESD STM5.3.1 states “In the CDM a component itself becomes charged (e.g., by sliding on a surface (tribocharging) or by electric field induction) and is rapidly discharged (by an ESD event) as it closely approaches a conductive object.”

In November 2002, Roger Peirce published an article entitled “The Most Common Causes of ESD Damage”. There were actually 23 causes. As the founder and president of ESD Technical Services, Roger had investigated hundreds of companies for over eight years. All 23 causes were CDM failure modes. So CDM is really not so new, it has just received a lot of attention in the last few years.

TACKLING CDMSo, what are the things companies should look at to improve their ESD control program regarding CDM? It would seem to be easy: don’t slide ESDS devices and assemblies unless grounded at all times, keep insulators at least 12” away from ESDS, and don’t allow ESDS items to make contact with a conductive surface. Seems simple, but in actual application . . . not so easy.

If the ESD control program has not used ionization that should be considered. If the ESDS items becomes charged, ionization will help neutralize the charge. The primary function of ionizers with regard to ESDS items are:

To remove / neutralize charges from process necessary insulators, which can charge ESDS items, thus creating the potential for a damaging CDM event

Remember that the PCB substrate is a process necessary insulator and can become charged during automated handling processes

To remove / neutralize charges from a charged, isolated/floating conductor, which, when grounded can result in a potentially damaging CDM event

Remember that during automated handling processes, the ESDS devices on the PCB are isolated or floating conductors

Application Photo Overhead Ionizer

The ESD Standards Committee has a Working Group (WG-17) which is currently involved with developing a Standard for Process Assessment to help the electronics community assess their manufacturing and handling processes to determine what levels of devices their process can handle. Once one fully understands where their process is with regards to ESDS devices and assemblies, they will have a clearer picture on what actions need to be taken to further improve the ESD Control Program.

If ionizers are already in use, the company should consider reducing the ionizer offset voltage limit of ±50 volts (the required limit in ANSI/ESD S20.20) to ±25 volts and maybe less, depending on the application and device sensitivity. Discharge times are user defined and should be considered for reducing the time required to neutralize a ± 1,000 volt charge to ± 100 volts.

The required limit for worksurfaces per ANSI/ESD S20.20 is less than 1 x 10^9 ohms with no lower limit. Most companies handling electronics should be following the recommendation of Worksurface standard ANSI/ESD S4.1 that the lower limit be 1 x 10^6 ohms. To combat CDM failures, all surfaces that might come into contact with ESDS items should be dissipative at the 1 x 10^6 to less than 1 x 10^9 ohms range used for worksurfaces where possible. Items such as Static Shielding bags will have a higher resistance on the interior & exterior surfaces, but it still must be less than 1 x 10^11 ohms.

It typically takes a ESD discharge greater than 2,000 or 3,000 volts for a person to feel the “zap”.

There is no exact voltage number where a person starts to feel a discharge. The ESD Association addresses this topic three times in the ESD Handbook ESD TR20.20 using these phrases:

“greater than 2000 volts”

“about 3,000 volts”

“exceed 3,000 volts”

The sensitivity of people is different and measuring the voltage is imprecise, so neither 2,000 nor 3,000 is to be an exact number.

Per ESD Handbook ESD TR20.20 Wrist Strap section 5.3.2.1 “Static electricity is a natural phenomenon that occurs in all climates and at all levels of relative humidity year round. Most people cannot feel an electrostatic discharge unless the static voltage is greater than 2000 volts.”

Per ESD Handbook ESD TR20.20 section 2.3 Nature of Static Electricity “The quantity, charge, is difficult for most people to visualize without some reference. As an example, an average person has a capacitance of about 100 picofarads (pF) and can feel a static discharge at their fingertips when the potential difference between their body and a grounded conductive object is about 3,000 volts (3 kV).”

Per ESD Handbook ESD TR20.20 ionizer section 5.3.6.5.3.3 Discharge Time and Product Sensitivity “Most personnel will not notice static discharges from the human body until they exceed 3,000 volts.”

The point, of course, is just because you cannot see or feel an ESD event, it does mean that ESD events are not occurring. Human beings are insensitive unless the ESD is several thousand volts. Many electronic components can be damaged by much smaller discharges.

Kaizen or continual improvement programs should often involve the ESD control program. When quality defects occur, many corrective actions will be improvements to the ESD control program to prevent recurrence.

We recommend using Protektive Pak impregnated corrugated which has a surface resistance of 1 x 10E6 < 1 x 10E9 ohms and is in the middle of the dissipative range. The ESD Association Packaging standard ANSI/ESD S541 section 7.2.2 includes “Packaging materials that are in intimate contact with devices should be dissipative.”

ProtektivePak In-Plant Handlers reduce ESD and physical defects, and can reduce work-in-process inventory as well as eliminating wasteful non-value added activities. As a Kaban container the In-Plant Handler can replace some or all documents. Instead of planners generating work orders, determine how many In-Plant Handlers to have on the shop floor and when cells are empty they signal the need to manufacture more of a particular item. Knowing the quantity of cells in the In-Plant Handler, one can quickly glance at the number of empty cells and know the count.

Protektive Pak impregnated corrugated has a buried shielding layer. For ESD shielding protection, with the lid in place, the In-Plant Handler can be moved or shipped outside the ESD Protected Area eliminating the need for ESD shielding bags. Per Packaging standard ANSI/ESD S541 section 6.2 Outside an EPA “Transportation of sensitive products outside of an EPA shall require packaging that provides:

Want to accomplish something important? A familiar formula is write a plan, select the speciﬁcations, and then periodically test to verify that the plan is being implemented according to the test
results. This is basically the requirements of an ESD control program, per the ESD Association standard, ANSI/ESD S20.20. This important standard, entitled Development of an Electrostatic Discharge Control Program, covers the requirements necessary to design, establish, implement, and maintain an ESD control program to protect electrical or electronic parts, assemblies and equipment susceptible to ESD damage.

S20.20 is a process document, and provides ESD control plan guidance; one of its requirements is having a “compliance veriﬁcation plan” as a component of the ESD control plan. Per S20.20, paragraph 6.1.3., Compliance Veriﬁcation Plan:

“A Compliance Veriﬁcation Plan shall be established to ensure the organization’s compliance with the requirements of the Plan. Formal audits or certiﬁcations shall be conducted in accordance with a Compliance Veriﬁcation Plan that identiﬁes the requirements to be veriﬁed, and the frequency at which those veriﬁcations must occur. Test equipment shall be selected to make measurements of appropriate properties of the technical requirements that are incorporated into the ESD program plan.”

To view more information on ESD Control Program Periodic Veriﬁcation CLICK HERE

What percentage of electronic failures are latent defects? What’s the cost to industry? According to the ESD Association “It is relatively easy with the proper equipment to confirm that a device has experienced catastrophic failure. Basic performance tests will substantiate device damage. However, latent defects are extremely difficult to prove or detect using current technology, especially after the device is assembled into a finished product.” So there is the view that, by definition, it is impossible to quantify the amount of latent damage. However, for most companies, the cost of customer returns and field service warranty expense greatly exceeds in-house scrap & re-work expense.

Per the ESD Association: “The age of electronics brought with it new problems associated with static electricity and electrostatic discharge. And, as electronic devices became faster and smaller, their sensitivity to ESD increased. Today, ESD impacts productivity and product reliability in virtually every aspect of today’s electronics environment. Industry experts have estimated average product losses due to static to range [up to] 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually.”

Some major companies report that 25% of all identified electronic part failure is due to ESD. As an ESD Control Program improves, a resulting decrease in unidentified field failures and ”no problem found” returns should occur. Reducing latent defect field failures is what allows companies to report return on investments of 10:1 from their ESD Control Programs.

ElectroStatic Discharge (ESD) is the hidden enemy within your factory. You cannot feel or see most ESD events but they can cause electronic components to fail or cause mysterious and annoying problems. There are two types of ESD damage: 1) Catastrophic failures, and 2) Latent defects. By definition, normal quality control inspections are able to identify catastrophic failures, but are not able to detect latent defects.

In general, the ESD susceptibility of modern electronics are more sensitive to ElectroStatic Discharge; that is the withstand voltages are lower. This is due to the drive for miniaturization particularly with electronic devices operating faster. Thus the semiconductor circuitry is getting smaller.

See November 2001 Evaluation Engineering Magazine article “ESD Control Program Development” “As the drive for miniaturization has reduced the width of electronic device structures to as small as 0.10 micrometer (equal to 0.0001 millimeter or 0.000004 inch), electronic components are being manufactured with increased ElectroStatic Discharge (ESD) susceptibility.”

What’s happening currently? Intel began selling its 32 nm processors in 2010 that would be 0.032 micrometer equal to 0.000032 millimeter or 0.00000128 inch.

See www.ESDA.org, the ESD Association’s latest White Paper “Electrostatic Discharge (ESD) Technology Roadmap – Revised April 2010” forecasts increased ESD sensitivities continuing the recent “trend, the ICs became even more sensitive to ESD events in the years between 2005 and 2009. Therefore, the prevailing trend is circuit performance at the expense of ESD protection levels.” The White Paper’s conclusions are:

“With devices becoming more sensitive through 2010-2015 and beyond, it is imperative that companies begin to scrutinize the ESD capabilities of their handling processes. Factory ESD control is expected to play an ever-increasing critical role as the industry is flooded with even more HBM and CDM sensitive designs. For people handling ESD sensitive devices, personnel grounding systems must be designed to limit body voltages to less than 100 volts.

To protect against metal-to-device discharges, all conductive elements that contact ESD sensitive devices must be grounded.

To limit the possibilities of a field induced CDM ESD event, users of ESD sensitive devices should ensure that the maximum voltage induced on their devices is kept below 50 volts.

See InCompliance Magazine May 2010 article by Dr. Terry L. Welsher The “Real” Cost of ESD Damage which includes “Recent data and experience reported by several companies and laboratories now suggest that many failures previously classified as EOS may instead be the result of ESD failures due to Charged Board Events (CBE). … Some companies have estimated that about 50% of failures originally designated as EOS were actually CBE or CDE.”

There are 3 classifications based on 3 different ESD models which are detailed standards from the ESD Association:http://esda.org/

(1) Human Body Model (HBM) [100 pF @ 1.5 kilohms], ESD STM5.1

(2) Charge Device Model (CDM) [4 pF/30 pF], ESD DS5.3.1

(3) Machine Model (MM) [200 pF @ 0 ohms], ESD STM5.2

Human Body ModelThe most common model is the HBM. This model simulates when a discharge occurs between a human (hand/finger) to a conductor (metal rail). The equivalent capacitance is 100 picofarads (100 x 10^-12 Farads) and equivalent resistance is 1,500 ohms to simulate a human body. The typical rise time of the current pulse (ESD) through a shorting wire averages 6 nanoseconds (6×10^-9 s) and larger for a higher resistant load. The peak current through a 500 ohm resistor averages 463 mA for a 1,000 volt pre-charge voltage.